As she tried to cram in a million and one things, I’d never seen my girl so hyper. Meanwhile, her little brother, Thomas, four, was unusually clingy.

What’s going on? I fretted.

Then, the doorbell rang. It was my ex-wife, Jane, ready to pick up the kids. Instantly, Serena stopped and put on her shoes, while Thomas dissolved into helpless tears.

Throwing his arms around me, he held on for dear life.

‘It’s going to be alright,’ I soothed, stroking his back. He was never usually so upset when he went back with his mum.

As I opened the door, my son gripped harder.

‘It’s okay,’ I said.

Jane had walked halfway down the driveway and was waiting for the kids.

Breezing past, Serena shot me a smile.

‘Bye Daddy,’ she said.

‘See you in a few days,’ I replied to my precious girl.

Harry was excited to be seeing his kids Serena and Thomas more often.

Harry Speath

As Jane’s car disappeared down the road, my heart sank. Separated for six months, I still loved her and desperately missed my children when they weren’t with me.

Since we’d split, Serena and Thomas stayed with me five nights out of every fortnight. Starting next week though, the court had decided we’d share custody – a week each.

I can’t wait, I thought.

In the meantime, I called the kids every Monday and Wednesday. But when I tried calling three days after their visit, it went to straight message bank. Two nights later, it happened again.

Awful thoughts ran through my mind.

Had Jane taken the kids away without telling me? But I never imagined she would do that.

Standing at the school gates on Friday afternoon, I waited patiently, but as the last student filed past, my stomach lurched. Racing to Jane’s mum’s house, where she lived with the kids, I rapped on

the door frantically.

‘Where are the kids?’ I asked Jane’s mum.

‘I haven’t seen them for over a week,’ she replied.

I left without getting any answers.

HArry with Serena on the day she was born.

Harry Speath

I was desperate to find them. Reliving our last moments together, I had a sick realisation.

They knew, I thought, playing back my boy’s sobs as we hugged goodbye.

A little older, Serena had tried to fit a lifetime of fun into three days.

As days turned into weeks, my heart ached.

How could you do this to us, Jane? I wondered. Our kids deserved better.

I called every Monday and Wednesday like usual, just in case.

Three weeks after they vanished, I spent Christmas alone, my kids’ unopened gifts under the twinkling tree.

‘They’ll be here when you come back,’ I whispered.

Thomas was only four when he disappeared with his big sister and their mum.

Harry Speath

Red tape made searching for my babies a nightmare. At the mercy of the court, I had to wait until February for a recovery order to be issued. An agonising three months later, my children were listed as missing.

‘Jane has family in southeast Queensland – that might be a good place to start,’ I told the police. A British passport holder, I prayed she hadn’t managed to take the kids overseas.

Without a paper trail, it was hard to know. And Jane hadn’t used her phone, or any of their Medicare cards. They’ve simply vanished, I thought, on my darkest days.

I started a Facebook page, Find Serena & Thomas Speath, and leads began to trickle in. Most I’d pass on to the authorities, but some I’d investigate myself.

In the meantime, another Christmas passed without my kids. I’d kept the tree up all year. Dejected, I took it down that Boxing Day. It tore my heart out, but it also steeled my resolve.

‘I’ll never stop looking for them,’ I vowed.

Serena and Thomas at the circus.

Harry Speath

Two-and-a-half years on, I’ve taken my search global, travelling to the UK, New Zealand and even Brazil. Pounding the pavement, I’ll speak to anyone who might have information.

I’m close, I’ve thought more than once. But each time, my hopes are dashed.

Back on home turf, I often take to the streets and hand out leaflets.

‘Have you seen my kids?’ I’ll ask. Every now and then, a sympathetic father stops.

On March 29, my girl turned eight. A month later, on April 27, my son had his seventh birthday.

Every year, I send my babies a card to let them know I’m thinking of them. Posting them to Jane’s mum’s house, I’m gutted when they’re quickly marked return to sender.

Last month, for International Missing Person’s Day, the Australian Federal Police released age-progressed photos of Serena and Thomas. Choking back tears, I couldn’t believe how much my kids had grown.

‘This is what I’m missing out on,’ I cried.

Serena and Thomas, if you’re reading this, your Daddy hasn’t forgotten you. I’m still looking for you and I always will.

And if you know anything, please do the right thing and come forward. Help me bring my babies home.